// lexer.el — el self-hosting lexer
//
// Tokenises an el source string into a list of token maps.
// Each token is a Map<String, Any> with keys:
//   "kind"  -> String  (e.g. "Int", "Ident", "Plus")
//   "value" -> String  (the raw text of the token)
//
// Entry point: fn lex(source: String) -> [Map<String, Any>]
//
// Uses native_string_chars to split the source into a chars list,
// then indexes it with native_list_get — avoids O(N²) string cloning.

// ── Character helpers ─────────────────────────────────────────────────────────

fn is_digit(ch: String) -> Bool {
    if ch == "0" { return true }
    if ch == "1" { return true }
    if ch == "2" { return true }
    if ch == "3" { return true }
    if ch == "4" { return true }
    if ch == "5" { return true }
    if ch == "6" { return true }
    if ch == "7" { return true }
    if ch == "8" { return true }
    if ch == "9" { return true }
    false
}

fn is_alpha(ch: String) -> Bool {
    if ch == "a" { return true }
    if ch == "b" { return true }
    if ch == "c" { return true }
    if ch == "d" { return true }
    if ch == "e" { return true }
    if ch == "f" { return true }
    if ch == "g" { return true }
    if ch == "h" { return true }
    if ch == "i" { return true }
    if ch == "j" { return true }
    if ch == "k" { return true }
    if ch == "l" { return true }
    if ch == "m" { return true }
    if ch == "n" { return true }
    if ch == "o" { return true }
    if ch == "p" { return true }
    if ch == "q" { return true }
    if ch == "r" { return true }
    if ch == "s" { return true }
    if ch == "t" { return true }
    if ch == "u" { return true }
    if ch == "v" { return true }
    if ch == "w" { return true }
    if ch == "x" { return true }
    if ch == "y" { return true }
    if ch == "z" { return true }
    if ch == "A" { return true }
    if ch == "B" { return true }
    if ch == "C" { return true }
    if ch == "D" { return true }
    if ch == "E" { return true }
    if ch == "F" { return true }
    if ch == "G" { return true }
    if ch == "H" { return true }
    if ch == "I" { return true }
    if ch == "J" { return true }
    if ch == "K" { return true }
    if ch == "L" { return true }
    if ch == "M" { return true }
    if ch == "N" { return true }
    if ch == "O" { return true }
    if ch == "P" { return true }
    if ch == "Q" { return true }
    if ch == "R" { return true }
    if ch == "S" { return true }
    if ch == "T" { return true }
    if ch == "U" { return true }
    if ch == "V" { return true }
    if ch == "W" { return true }
    if ch == "X" { return true }
    if ch == "Y" { return true }
    if ch == "Z" { return true }
    false
}

fn is_alnum_or_underscore(ch: String) -> Bool {
    if is_digit(ch) { return true }
    if is_alpha(ch) { return true }
    if ch == "_" { return true }
    false
}

fn is_whitespace(ch: String) -> Bool {
    if ch == " " { return true }
    if ch == "\t" { return true }
    if ch == "\n" { return true }
    if ch == "\r" { return true }
    false
}

fn make_tok(kind: String, value: String) -> Map<String, Any> {
    { "kind": kind, "value": value }
}

// ── Keyword lookup ────────────────────────────────────────────────────────────

fn keyword_kind(word: String) -> String {
    if word == "let" { return "Let" }
    if word == "fn" { return "Fn" }
    if word == "type" { return "Type" }
    if word == "enum" { return "Enum" }
    if word == "match" { return "Match" }
    if word == "return" { return "Return" }
    if word == "if" { return "If" }
    if word == "else" { return "Else" }
    if word == "for" { return "For" }
    if word == "in" { return "In" }
    if word == "while" { return "While" }
    if word == "import" { return "Import" }
    if word == "from" { return "From" }
    if word == "as" { return "As" }
    if word == "with" { return "With" }
    if word == "sealed" { return "Sealed" }
    if word == "activate" { return "Activate" }
    if word == "where" { return "Where" }
    if word == "test" { return "Test" }
    if word == "seed" { return "Seed" }
    if word == "assert" { return "Assert" }
    if word == "protocol" { return "Protocol" }
    if word == "impl" { return "Impl" }
    if word == "retry" { return "Retry" }
    if word == "times" { return "Times" }
    if word == "fallback" { return "Fallback" }
    if word == "reason" { return "Reason" }
    if word == "parallel" { return "Parallel" }
    if word == "trace" { return "Trace" }
    if word == "requires" { return "Requires" }
    if word == "deploy" { return "Deploy" }
    if word == "to" { return "To" }
    if word == "via" { return "Via" }
    if word == "target" { return "Target" }
    if word == "true" { return "Bool" }
    if word == "false" { return "Bool" }
    if word == "cgi" { return "Cgi" }
    if word == "service" { return "Service" }
    if word == "manager" { return "Manager" }
    if word == "engine" { return "Engine" }
    if word == "accessor" { return "Accessor" }
    if word == "vessel" { return "Vessel" }
    ""
}

// ── Scan helpers ──────────────────────────────────────────────────────────────
// All scan helpers receive the chars list and total length.

// scan_digits — advance i while chars[i] is a digit
// Returns { "text": ..., "pos": i }
fn scan_digits(chars: [String], start: Int, total: Int) -> Map<String, Any> {
    let i = start
    let text = ""
    let running = true
    while running {
        if i >= total {
            let running = false
        } else {
            let ch: String = native_list_get(chars, i)
            if is_digit(ch) {
                let text = text + ch
                let i = i + 1
            } else {
                let running = false
            }
        }
    }
    { "text": text, "pos": i }
}

// scan_ident — advance i while chars[i] is alphanumeric or underscore
fn scan_ident(chars: [String], start: Int, total: Int) -> Map<String, Any> {
    let i = start
    let text = ""
    let running = true
    while running {
        if i >= total {
            let running = false
        } else {
            let ch: String = native_list_get(chars, i)
            if is_alnum_or_underscore(ch) {
                let text = text + ch
                let i = i + 1
            } else {
                let running = false
            }
        }
    }
    { "text": text, "pos": i }
}

// ── Code-bearing string detection + comment strip ────────────────────────────
// Inline JS/CSS literals embedded in El source (e.g. <script>…</script> blobs
// or stylesheet payloads inside string literals) carry their own line and
// block comments. Those comments leak into the served HTML and reveal build
// notes the visitor should never see. We strip them at the lexer so every
// downstream consumer (codegen-c, codegen-js, parser) gets the cleaned form.
//
// looks_like_code — heuristic gate so we only strip strings that actually
// embed JS or CSS. Plain prose, hex blobs, JSON, etc. pass through verbatim.

fn substr_at(chars: [String], start: Int, total: Int, needle: String) -> Bool {
    let nchars: [String] = native_string_chars(needle)
    let nlen: Int = native_list_len(nchars)
    if start + nlen > total { return false }
    let i = 0
    let matched = true
    while i < nlen {
        let a: String = native_list_get(chars, start + i)
        let b: String = native_list_get(nchars, i)
        if a == b { let i = i + 1 } else { let matched = false; let i = nlen }
    }
    matched
}

fn str_has(s: String, needle: String) -> Bool {
    let chars: [String] = native_string_chars(s)
    let total: Int = native_list_len(chars)
    let i = 0
    let found = false
    while i < total {
        if substr_at(chars, i, total, needle) {
            let found = true
            let i = total
        } else {
            let i = i + 1
        }
    }
    found
}

fn looks_like_code(s: String) -> Bool {
    if str_has(s, "<script") { return true }
    if str_has(s, "<style") { return true }
    if str_has(s, "function") {
        if str_has(s, ";") { return true }
    }
    false
}

// strip_code_comments — character-by-character walk. Tracks JS string state
// (single, double, backtick) and never strips inside one. Backslash escapes
// inside JS strings consume the next char verbatim. URLs like https:// are
// preserved by checking the previous char before treating // as a line
// comment opener: if the char immediately before '/' is ':', emit the '/'
// literally and advance one position.
fn strip_code_comments(s: String) -> String {
    let chars: [String] = native_string_chars(s)
    let total: Int = native_list_len(chars)
    let out = ""
    let i = 0
    let in_squote = false
    let in_dquote = false
    let in_btick = false
    let prev = ""
    while i < total {
        let ch: String = native_list_get(chars, i)
        let in_js_string = false
        if in_squote { let in_js_string = true }
        if in_dquote { let in_js_string = true }
        if in_btick { let in_js_string = true }

        if in_js_string {
            // Backslash escape: consume next char verbatim regardless of which.
            if ch == "\\" {
                let out = out + ch
                let next_i = i + 1
                if next_i < total {
                    let nc: String = native_list_get(chars, next_i)
                    let out = out + nc
                    let prev = nc
                    let i = next_i + 1
                } else {
                    let prev = ch
                    let i = next_i
                }
            } else {
                if in_squote {
                    if ch == "'" { let in_squote = false }
                } else {
                    if in_dquote {
                        if ch == "\"" { let in_dquote = false }
                    } else {
                        if in_btick {
                            if ch == "`" { let in_btick = false }
                        }
                    }
                }
                let out = out + ch
                let prev = ch
                let i = i + 1
            }
        } else {
            // Not in a JS string. Check for comment openers.
            let next_i = i + 1
            let next_ch = ""
            if next_i < total {
                let next_ch: String = native_list_get(chars, next_i)
            }

            if ch == "/" {
                if next_ch == "/" {
                    // URL guard: prev char ':' means this is "://", not a comment.
                    if prev == ":" {
                        let out = out + ch
                        let prev = ch
                        let i = i + 1
                    } else {
                        // Skip until newline (newline itself is preserved so
                        // surrounding line counts/structure stay sane).
                        let i = i + 2
                        let scanning = true
                        while scanning {
                            if i >= total {
                                let scanning = false
                            } else {
                                let lc: String = native_list_get(chars, i)
                                if lc == "\n" {
                                    let scanning = false
                                } else {
                                    let i = i + 1
                                }
                            }
                        }
                        let prev = ""
                    }
                } else {
                    if next_ch == "*" {
                        // Skip until matching "*/".
                        let i = i + 2
                        let scanning2 = true
                        while scanning2 {
                            if i >= total {
                                let scanning2 = false
                            } else {
                                let bc: String = native_list_get(chars, i)
                                if bc == "*" {
                                    let after = i + 1
                                    if after < total {
                                        let nc2: String = native_list_get(chars, after)
                                        if nc2 == "/" {
                                            let i = after + 1
                                            let scanning2 = false
                                        } else {
                                            let i = i + 1
                                        }
                                    } else {
                                        let i = i + 1
                                    }
                                } else {
                                    let i = i + 1
                                }
                            }
                        }
                        let prev = ""
                    } else {
                        let out = out + ch
                        let prev = ch
                        let i = i + 1
                    }
                }
            } else {
                // Open a JS string?
                if ch == "'" {
                    let in_squote = true
                    let out = out + ch
                    let prev = ch
                    let i = i + 1
                } else {
                    if ch == "\"" {
                        let in_dquote = true
                        let out = out + ch
                        let prev = ch
                        let i = i + 1
                    } else {
                        if ch == "`" {
                            let in_btick = true
                            let out = out + ch
                            let prev = ch
                            let i = i + 1
                        } else {
                            let out = out + ch
                            let prev = ch
                            let i = i + 1
                        }
                    }
                }
            }
        }
    }
    out
}

// scan_string — scan a quoted string literal, handling \" escapes.
// Starts AFTER the opening quote. Returns { "text": content, "pos": i_after_close }
fn scan_string(chars: [String], start: Int, total: Int) -> Map<String, Any> {
    let i = start
    let text = ""
    let running = true
    while running {
        if i >= total {
            let running = false
        } else {
            let ch: String = native_list_get(chars, i)
            if ch == "\\" {
                // escape: peek next char
                let next_i = i + 1
                if next_i < total {
                    let next_ch: String = native_list_get(chars, next_i)
                    if next_ch == "\"" {
                        let text = text + "\""
                        let i = next_i + 1
                    } else {
                        if next_ch == "n" {
                            let text = text + "\n"
                            let i = next_i + 1
                        } else {
                            if next_ch == "t" {
                                let text = text + "\t"
                                let i = next_i + 1
                            } else {
                                if next_ch == "r" {
                                    let text = text + "\r"
                                    let i = next_i + 1
                                } else {
                                    if next_ch == "\\" {
                                        let text = text + "\\"
                                        let i = next_i + 1
                                    } else {
                                        let text = text + next_ch
                                        let i = next_i + 1
                                    }
                                }
                            }
                        }
                    }
                } else {
                    let i = i + 1
                }
            } else {
                if ch == "\"" {
                    let i = i + 1
                    let running = false
                } else {
                    let text = text + ch
                    let i = i + 1
                }
            }
        }
    }
    { "text": text, "pos": i }
}

// ── Main lexer ────────────────────────────────────────────────────────────────

fn lex(source: String) -> [Map<String, Any>] {
    let chars: [String] = native_string_chars(source)
    let total: Int = native_list_len(chars)
    let tokens: [Map<String, Any>] = native_list_empty()
    let i: Int = 0

    while i < total {
        let ch: String = native_list_get(chars, i)

        // Skip whitespace
        if is_whitespace(ch) {
            let i = i + 1
        } else {
            // Line comments: //
            if ch == "/" {
                let next_i = i + 1
                if next_i < total {
                    let next_ch: String = native_list_get(chars, next_i)
                    if next_ch == "/" {
                        // skip to end of line
                        let i = i + 2
                        let running2 = true
                        while running2 {
                            if i >= total {
                                let running2 = false
                            } else {
                                let lch: String = native_list_get(chars, i)
                                if lch == "\n" {
                                    let running2 = false
                                } else {
                                    let i = i + 1
                                }
                            }
                        }
                    } else {
                        let tokens = native_list_append(tokens, make_tok("Slash", "/"))
                        let i = i + 1
                    }
                } else {
                    let tokens = native_list_append(tokens, make_tok("Slash", "/"))
                    let i = i + 1
                }
            } else {
                // String literal
                if ch == "\"" {
                    let result = scan_string(chars, i + 1, total)
                    let str_text: String = result["text"]
                    let new_pos: Int = result["pos"]
                    // Compile-time scrub: strings that embed JS or CSS get
                    // their // line comments and /* block comments stripped
                    // before the token reaches the parser. Plain prose passes
                    // through untouched.
                    let clean_text = str_text
                    if looks_like_code(str_text) {
                        let clean_text = strip_code_comments(str_text)
                    }
                    let tokens = native_list_append(tokens, make_tok("Str", clean_text))
                    let i = new_pos
                } else {
                    // Number literal
                    if is_digit(ch) {
                        let result = scan_digits(chars, i, total)
                        let num_text: String = result["text"]
                        let new_pos: Int = result["pos"]
                        // check for float (dot followed by digit)
                        if new_pos < total {
                            let dot_ch: String = native_list_get(chars, new_pos)
                            if dot_ch == "." {
                                let after_dot = new_pos + 1
                                if after_dot < total {
                                    let after_dot_ch: String = native_list_get(chars, after_dot)
                                    if is_digit(after_dot_ch) {
                                        let frac_result = scan_digits(chars, after_dot, total)
                                        let frac_text: String = frac_result["text"]
                                        let frac_pos: Int = frac_result["pos"]
                                        let tokens = native_list_append(tokens, make_tok("Float", num_text + "." + frac_text))
                                        let i = frac_pos
                                    } else {
                                        let tokens = native_list_append(tokens, make_tok("Int", num_text))
                                        let i = new_pos
                                    }
                                } else {
                                    let tokens = native_list_append(tokens, make_tok("Int", num_text))
                                    let i = new_pos
                                }
                            } else {
                                let tokens = native_list_append(tokens, make_tok("Int", num_text))
                                let i = new_pos
                            }
                        } else {
                            let tokens = native_list_append(tokens, make_tok("Int", num_text))
                            let i = new_pos
                        }
                    } else {
                        // Identifier or keyword
                        if is_alpha(ch) || ch == "_" {
                            let result = scan_ident(chars, i, total)
                            let word: String = result["text"]
                            let new_pos: Int = result["pos"]
                            let kw = keyword_kind(word)
                            if kw == "" {
                                let tokens = native_list_append(tokens, make_tok("Ident", word))
                            } else {
                                let tokens = native_list_append(tokens, make_tok(kw, word))
                            }
                            let i = new_pos
                        } else {
                            // Multi-char and single-char operators/delimiters
                            let peek_i = i + 1
                            let peek_ch = ""
                            if peek_i < total {
                                let peek_ch: String = native_list_get(chars, peek_i)
                            }

                            if ch == "=" {
                                if peek_ch == "=" {
                                    let tokens = native_list_append(tokens, make_tok("EqEq", "=="))
                                    let i = i + 2
                                } else {
                                    if peek_ch == ">" {
                                        let tokens = native_list_append(tokens, make_tok("FatArrow", "=>"))
                                        let i = i + 2
                                    } else {
                                        let tokens = native_list_append(tokens, make_tok("Eq", "="))
                                        let i = i + 1
                                    }
                                }
                            } else {
                                if ch == "!" {
                                    if peek_ch == "=" {
                                        let tokens = native_list_append(tokens, make_tok("NotEq", "!="))
                                        let i = i + 2
                                    } else {
                                        let tokens = native_list_append(tokens, make_tok("Not", "!"))
                                        let i = i + 1
                                    }
                                } else {
                                    if ch == "<" {
                                        if peek_ch == "=" {
                                            let tokens = native_list_append(tokens, make_tok("LtEq", "<="))
                                            let i = i + 2
                                        } else {
                                            let tokens = native_list_append(tokens, make_tok("Lt", "<"))
                                            let i = i + 1
                                        }
                                    } else {
                                        if ch == ">" {
                                            if peek_ch == "=" {
                                                let tokens = native_list_append(tokens, make_tok("GtEq", ">="))
                                                let i = i + 2
                                            } else {
                                                let tokens = native_list_append(tokens, make_tok("Gt", ">"))
                                                let i = i + 1
                                            }
                                        } else {
                                            if ch == "&" {
                                                if peek_ch == "&" {
                                                    let tokens = native_list_append(tokens, make_tok("And", "&&"))
                                                    let i = i + 2
                                                } else {
                                                    let i = i + 1
                                                }
                                            } else {
                                                if ch == "|" {
                                                    if peek_ch == "|" {
                                                        let tokens = native_list_append(tokens, make_tok("Or", "||"))
                                                        let i = i + 2
                                                    } else {
                                                        if peek_ch == ">" {
                                                            let tokens = native_list_append(tokens, make_tok("PipeOp", "|>"))
                                                            let i = i + 2
                                                        } else {
                                                            let tokens = native_list_append(tokens, make_tok("Pipe", "|"))
                                                            let i = i + 1
                                                        }
                                                    }
                                                } else {
                                                    if ch == "-" {
                                                        if peek_ch == ">" {
                                                            let tokens = native_list_append(tokens, make_tok("Arrow", "->"))
                                                            let i = i + 2
                                                        } else {
                                                            let tokens = native_list_append(tokens, make_tok("Minus", "-"))
                                                            let i = i + 1
                                                        }
                                                    } else {
                                                        if ch == ":" {
                                                            if peek_ch == ":" {
                                                                let tokens = native_list_append(tokens, make_tok("ColonColon", "::"))
                                                                let i = i + 2
                                                            } else {
                                                                let tokens = native_list_append(tokens, make_tok("Colon", ":"))
                                                                let i = i + 1
                                                            }
                                                        } else {
                                                            if ch == "+" {
                                                                let tokens = native_list_append(tokens, make_tok("Plus", "+"))
                                                                let i = i + 1
                                                            } else {
                                                                if ch == "*" {
                                                                    let tokens = native_list_append(tokens, make_tok("Star", "*"))
                                                                    let i = i + 1
                                                                } else {
                                                                if ch == "%" {
                                                                    let tokens = native_list_append(tokens, make_tok("Percent", "%"))
                                                                    let i = i + 1
                                                                } else {
                                                                    if ch == "(" {
                                                                        let tokens = native_list_append(tokens, make_tok("LParen", "("))
                                                                        let i = i + 1
                                                                    } else {
                                                                        if ch == ")" {
                                                                            let tokens = native_list_append(tokens, make_tok("RParen", ")"))
                                                                            let i = i + 1
                                                                        } else {
                                                                            if ch == "{" {
                                                                                let tokens = native_list_append(tokens, make_tok("LBrace", "{"))
                                                                                let i = i + 1
                                                                            } else {
                                                                                if ch == "}" {
                                                                                    let tokens = native_list_append(tokens, make_tok("RBrace", "}"))
                                                                                    let i = i + 1
                                                                                } else {
                                                                                    if ch == "[" {
                                                                                        let tokens = native_list_append(tokens, make_tok("LBracket", "["))
                                                                                        let i = i + 1
                                                                                    } else {
                                                                                        if ch == "]" {
                                                                                            let tokens = native_list_append(tokens, make_tok("RBracket", "]"))
                                                                                            let i = i + 1
                                                                                        } else {
                                                                                            if ch == "," {
                                                                                                let tokens = native_list_append(tokens, make_tok("Comma", ","))
                                                                                                let i = i + 1
                                                                                            } else {
                                                                                                if ch == "." {
                                                                                                    let tokens = native_list_append(tokens, make_tok("Dot", "."))
                                                                                                    let i = i + 1
                                                                                                } else {
                                                                                                    if ch == ";" {
                                                                                                        let tokens = native_list_append(tokens, make_tok("Semicolon", ";"))
                                                                                                        let i = i + 1
                                                                                                    } else {
                                                                                                        if ch == "@" {
                                                                                                            let tokens = native_list_append(tokens, make_tok("At", "@"))
                                                                                                            let i = i + 1
                                                                                                        } else {
                                                                                                            if ch == "?" {
                                                                                                                let tokens = native_list_append(tokens, make_tok("QuestionMark", "?"))
                                                                                                                let i = i + 1
                                                                                                            } else {
                                                                                                                // unknown char — skip
                                                                                                                let i = i + 1
                                                                                                            }
                                                                                                        }
                                                                                                    }
                                                                                                }
                                                                                            }
                                                                                        }
                                                                                    }
                                                                                }
                                                                            }
                                                                        }
                                                                    }
                                                                }
                                                                }
                                                            }
                                                        }
                                                    }
                                                }
                                            }
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }

    let tokens = native_list_append(tokens, make_tok("Eof", ""))
    tokens
}