// compiler.el — el self-hosting compiler pipeline
//
// Wires lexer -> parser -> codegen into a single compile() function.
// This is the bootstrap entry point: compiled once by the Rust el-compiler,
// then self-hosted from that point forward.
//
// Two backends:
//   - C    (default)   compile()    -> emits C source linked against el_runtime.c
//   - JS   (--target=js) compile_js() -> emits JS source linked against el_runtime.js
//
// Compile the C output with:
//   cc -o <prog> <prog>.c el_runtime.c
//
// Run the JS output with:
//   node <prog>.js   (after copying el_runtime.js next to it)

import "lexer.el"
import "parser.el"
import "codegen.el"
import "codegen-js.el"

// compile — full pipeline (C target): source string -> C source string
fn compile(source: String) -> String {
    let tokens: [Map<String, Any>] = lex(source)
    let stmts: [Map<String, Any>] = parse(tokens)
    // Token list is no longer needed after parsing — release it to free memory
    // before codegen allocates its own working data on large source files.
    el_release(tokens)
    codegen(stmts, source)
}

// compile_js — full pipeline (JS target, module mode): source string -> JS source string
fn compile_js(source: String) -> String {
    let tokens: [Map<String, Any>] = lex(source)
    let stmts: [Map<String, Any>] = parse(tokens)
    // Token list is no longer needed after parsing — release it to free memory.
    el_release(tokens)
    codegen_js(stmts, source)
}

// compile_js_with_bundle — JS target in bundle mode.
// Reads el_runtime.js from runtime_path and inlines it inside an IIFE.
fn compile_js_with_bundle(source: String, runtime_path: String) -> String {
    let tokens: [Map<String, Any>] = lex(source)
    let stmts: [Map<String, Any>] = parse(tokens)
    el_release(tokens)
    let runtime_content: String = fs_read(runtime_path)
    if str_eq(runtime_content, "") {
        println("el-compiler: warning: --bundle: could not read runtime at " + runtime_path)
        println("el-compiler: warning: bundle output will be incomplete")
    }
    codegen_js_bundle(stmts, source, runtime_content)
}

// compile_dispatch — pick a backend based on the requested target.
//   tgt = "c"  | "js"
// (The parameter is named `tgt` because `target` is a reserved keyword
//  in El's lexer — it would be tokenised as `Target`, breaking the
//  parser's identifier resolution.)
fn compile_dispatch(tgt: String, source: String) -> String {
    if str_eq(tgt, "js") { return compile_js(source) }
    compile(source)
}

// compile_dispatch_bundle — like compile_dispatch but bundle mode for JS.
fn compile_dispatch_bundle(tgt: String, source: String, runtime_path: String) -> String {
    if str_eq(tgt, "js") { return compile_js_with_bundle(source, runtime_path) }
    compile(source)
}

// Detect a `--target=<lang>` flag in argv and return the target.
// Returns "c" if none specified or unrecognized.
fn detect_target(argv: [String]) -> String {
    let n: Int = native_list_len(argv)
    let i = 0
    while i < n {
        let a: String = native_list_get(argv, i)
        if str_starts_with(a, "--target=") {
            let v: String = str_slice(a, 9, str_len(a))
            return v
        }
        let i = i + 1
    }
    return "c"
}

// Strip flags from argv, leaving only positional arguments.
fn strip_flags(argv: [String]) -> [String] {
    let out: [String] = native_list_empty()
    let n: Int = native_list_len(argv)
    let i = 0
    while i < n {
        let a: String = native_list_get(argv, i)
        if !str_starts_with(a, "--") {
            let out = native_list_append(out, a)
        }
        let i = i + 1
    }
    return out
}

// Detect --emit-header flag in argv.
fn detect_emit_header(argv: [String]) -> Bool {
    let n: Int = native_list_len(argv)
    let i = 0
    while i < n {
        let a: String = native_list_get(argv, i)
        if str_eq(a, "--emit-header") { return true }
        let i = i + 1
    }
    return false
}

// Detect --bundle flag in argv.
fn detect_bundle(argv: [String]) -> Bool {
    let n: Int = native_list_len(argv)
    let i = 0
    while i < n {
        let a: String = native_list_get(argv, i)
        if str_eq(a, "--bundle") { return true }
        let i = i + 1
    }
    return false
}

// Resolve the runtime path for --bundle mode.
// Looks for el_runtime.js next to the source file first;
// if not found there, looks next to the elc binary itself.
// Returns "" if not found anywhere (caller emits a warning).
fn resolve_runtime_path(src_path: String) -> String {
    let src_dir: String = dirname_of(src_path)
    let candidate: String = src_dir + "/el_runtime.js"
    let existing: String = fs_read(candidate)
    if !str_eq(existing, "") {
        return candidate
    }
    return ""
}

// Reconstruct an El type annotation string from a parsed type node.
fn type_node_to_el(t: Map<String, Any>) -> String {
    let k: String = t["kind"]
    if str_eq(k, "Simple") { return t["name"] }
    if str_eq(k, "List") {
        let inner: String = type_node_to_el(t["inner"])
        return "[" + inner + "]"
    }
    if str_eq(k, "Map") {
        let kt: String = type_node_to_el(t["key"])
        let vt: String = type_node_to_el(t["val"])
        return "Map<" + kt + ", " + vt + ">"
    }
    "Any"
}

// emit_header — write a .elh file from parsed statements.
// Scans for FnDef nodes and emits 'extern fn' declarations.
fn emit_header(stmts: [Map<String, Any>], hdr_path: String) -> Void {
    let n: Int = native_list_len(stmts)
    let i = 0
    let parts: [String] = native_list_empty()
    let parts = native_list_append(parts, "// auto-generated by elc --emit-header — do not edit\n")
    while i < n {
        let stmt = native_list_get(stmts, i)
        let kind: String = stmt["stmt"]
        if str_eq(kind, "FnDef") {
            let name: String = stmt["name"]
            if !str_eq(name, "main") {
                let params = stmt["params"]
                let ret_type: String = stmt["ret_type"]
                // build param list
                let np: Int = native_list_len(params)
                let pi = 0
                let param_parts: [String] = native_list_empty()
                while pi < np {
                    let param = native_list_get(params, pi)
                    let pname: String = param["name"]
                    let ptype: String = param["type"]
                    if str_eq(ptype, "") { let ptype = "Any" }
                    let param_parts = native_list_append(param_parts, pname + ": " + ptype)
                    let pi = pi + 1
                }
                let params_str: String = str_join(param_parts, ", ")
                let ret_str: String = ret_type
                if str_eq(ret_str, "") { let ret_str = "Any" }
                let sig: String = "extern fn " + name + "(" + params_str + ") -> " + ret_str
                let parts = native_list_append(parts, sig + "\n")
            }
        }
        let i = i + 1
    }
    let content: String = str_join(parts, "")
    let ok: Bool = fs_write(hdr_path, content)
}

// ── Import resolution ────────────────────────────────────────────────────────
//
// elc supports two forms of import:
//   import "path/to/file.el"       — quoted relative path
//   from module import { Name }    — bare module name resolves to module.el
//                                    in the entry source's directory
//
// Codegen treats Import statements as no-ops (declarations only), so to
// actually link bodies across files we textually concatenate every imported
// source ahead of the entry source before lex/parse. resolve_imports does a
// depth-first traversal with deduplication so any module that gets pulled in
// transitively is included exactly once.

fn dirname_of(path: String) -> String {
    let n: Int = str_len(path)
    let i: Int = n - 1
    while i >= 0 {
        let c: String = str_slice(path, i, i + 1)
        if str_eq(c, "/") {
            return str_slice(path, 0, i)
        }
        let i = i - 1
    }
    return "."
}

// Extract the resolved file path from a single trimmed source line. Returns
// "" if the line is not an import.
fn parse_import_line(trimmed: String, dir: String) -> String {
    if str_starts_with(trimmed, "import \"") {
        let after: String = str_slice(trimmed, 8, str_len(trimmed))
        let q: Int = str_index_of(after, "\"")
        if q > 0 {
            let mod: String = str_slice(after, 0, q)
            return dir + "/" + mod
        }
    }
    if str_starts_with(trimmed, "from ") {
        let after: String = str_slice(trimmed, 5, str_len(trimmed))
        // module name is the first whitespace-delimited token
        let sp: Int = str_index_of(after, " ")
        if sp > 0 {
            let mod_raw: String = str_slice(after, 0, sp)
            let mod: String = str_trim(mod_raw)
            if !str_eq(mod, "") {
                return dir + "/" + mod + ".el"
            }
        }
    }
    return ""
}

// Recursively resolve imports starting from src_path. Returns the combined
// source text with every imported module's body inlined ahead of the entry
// source, deduplicated by absolute path. Uses state_set to track which paths
// have already been pulled in for this run.
//
// Accumulates chunks into lists and joins once at the end to avoid the O(n²)
// memory growth caused by repeated `prefix = prefix + chunk` concatenation.
fn resolve_imports(src_path: String) -> String {
    let seen_key: String = "__elc_imp__:" + src_path
    let already: String = state_get(seen_key)
    if !str_eq(already, "") { return "" }
    state_set(seen_key, "1")

    let source: String = fs_read(src_path)
    let dir: String = dirname_of(src_path)
    let lines: [String] = str_split(source, "\n")
    let n: Int = native_list_len(lines)

    // Collect chunks into lists — O(1) amortized per append.
    // Join once at the end — O(n) single pass.
    let prefix_chunks: [String] = native_list_empty()
    let body_chunks: [String] = native_list_empty()
    let i: Int = 0
    while i < n {
        let line: String = native_list_get(lines, i)
        let trimmed: String = str_trim(line)
        let imp_path: String = parse_import_line(trimmed, dir)
        if !str_eq(imp_path, "") {
            // Use pre-compiled header if available (separate compilation).
            // Only check .elh for imported files — never for the entry file itself.
            let imp_elh_path: String = str_slice(imp_path, 0, str_len(imp_path) - 3) + ".elh"
            let imp_elh: String = fs_read(imp_elh_path)
            if !str_eq(imp_elh, "") {
                // Header exists: mark the .el as seen (so it won't be re-inlined
                // if something else also imports it) and use the header text.
                let seen_imp_key: String = "__elc_imp__:" + imp_path
                state_set(seen_imp_key, "1")
                let prefix_chunks = native_list_append(prefix_chunks, imp_elh)
            } else {
                let imp_body: String = resolve_imports(imp_path)
                let prefix_chunks = native_list_append(prefix_chunks, imp_body)
            }
        } else {
            let body_chunks = native_list_append(body_chunks, line + "\n")
        }
        let i = i + 1
    }
    return str_join(prefix_chunks, "") + str_join(body_chunks, "")
}

// main — CLI entry point.
//
//   elc <source.el>                               # emit C to stdout
//   elc --target=js <source.el>                   # emit JS (module) to stdout
//   elc --target=js --bundle <source.el>          # emit self-contained JS (IIFE) to stdout
//   elc --target=c  <source.el> <out.c>           # write C to file
//   elc --target=js <source.el> <out.js>          # write JS to file
//   elc --target=js --bundle <source.el> <out.js> # write bundled JS to file
fn main() -> Void {
    let argv: [String] = args()
    // Use `tgt` not `target`: `target` is a reserved keyword in the lexer
    // (Section 1.5 of the language spec). detect_target itself is fine
    // because the function-name position has no token-class restriction.
    let tgt: String = detect_target(argv)
    let do_emit_header: Bool = detect_emit_header(argv)
    let do_bundle: Bool = detect_bundle(argv)
    let positional: [String] = strip_flags(argv)
    let argc: Int = native_list_len(positional)
    if argc < 1 {
        println("el-compiler: usage: elc [--target=c|js] [--bundle] [--emit-header] <source.el> [<output>]")
        exit(1)
    }
    let src_path: String = native_list_get(positional, 0)

    // When --emit-header is requested, parse the source file directly
    // (without inlining imports) and write out a .elh file alongside the .c.
    if do_emit_header {
        let raw_source: String = fs_read(src_path)
        let hdr_tokens: [Map<String, Any>] = lex(raw_source)
        let hdr_stmts: [Map<String, Any>] = parse(hdr_tokens)
        el_release(hdr_tokens)
        let hdr_path: String = str_slice(src_path, 0, str_len(src_path) - 3) + ".elh"
        emit_header(hdr_stmts, hdr_path)
        el_release(hdr_stmts)
    }

    let source: String = resolve_imports(src_path)
    let out: String = ""
    if do_bundle {
        let runtime_path: String = resolve_runtime_path(src_path)
        let out = compile_dispatch_bundle(tgt, source, runtime_path)
    } else {
        let out = compile_dispatch(tgt, source)
    }
    if argc >= 2 {
        let out_path: String = native_list_get(positional, 1)
        let ok: Bool = fs_write(out_path, out)
        if ok {
            exit(0)
        } else {
            println("el-compiler: failed to write output")
            exit(1)
        }
    }
    // No output path: codegen streamed to stdout already; out is "".
}