// simple-ts-highlighter.ts — regex-only, self-hostable

export type TokenType =
    | "string" | "number" | "keyword" | "boolean" | "null" | "undefined"
    | "comment" | "identifier" | "punctuation" | "whitespace" | "unknown"

export type Token = { type: TokenType; value: string; start: number; end: number }
export type Program = { type: "Program"; tokens: Token[] }

const RE = {
    // regex literal: /.../flags   (handles escapes and [...] classes; still simple)
    regex: /^\/(?![/*])(?:\\.|\[(?:\\.|[^\]\\])*\]|[^\\/\n\r])+\/[a-zA-Z]*/,

    // comments
    lineComment: /^\/\/[^\n\r]*/,
    blockComment: /^\/\*[\s\S]*?\*\//,

    // strings
    sng: /^'(?:\\.|[^'\\])*'/,
    dbl: /^"(?:\\.|[^"\\])*"/,
    bkt: /^`(?:\\.|[^`\\])*`/,

    // numbers
    number: /^(?:0[xX][0-9a-fA-F]+|0[bB][01]+|0[oO][0-7]+|\d+(?:\.\d+)?(?:[eE][+\-]?\d+)?)/,

    // literals
    boolNullUndef: /^(?:true|false|null|undefined)\b/,

    // keywords
    keywords: /^(?:async|await|break|case|catch|class|const|continue|debugger|default|delete|do|else|enum|export|extends|finally|for|function|if|import|in|instanceof|let|new|return|super|switch|this|throw|try|typeof|var|void|while|with|yield|as|implements|interface|package|private|protected|public|readonly|abstract|declare|type|from|of)\b/,

    // identifier / punct / whitespace
    ident: /^[A-Za-z_$][A-Za-z0-9_$]*/,
    punct: /^[()[\]{}.,;:?~!%^&*+\-=/|<>]+/,
    ws: /^\s+/,
}

const types = ["string", "number", "boolean", "any", "void"]

export function highlight(code: string): string {
    const tokens = tokenize(code).tokens
    return `<style> .string { color: #C62828; } .number { color: #C4A000; } .keyword { color: #7C3AED; } .comment { color: #E91E63; } </style>` + tokens.map(t => tokenToHTML(t)).join("")
}

export function tokenize(src: string): Program {
    const tokens: Token[] = []
    let i = 0

    const eat = (re: RegExp): string | null => {
        const m = re.exec(src.slice(i))
        return m ? m[0] : null
    }

    while (i < src.length) {
        let v: string | null

        // If current char is '/', disambiguate regex/comment upfront
        if (src[i] === "/") {
            if (src[i + 1] === "/") {
                v = eat(RE.lineComment)
                if (v) { tokens.push({ type: "comment", value: v, start: i, end: i + v.length }); i += v.length; continue }
            } else if (src[i + 1] === "*") {
                v = eat(RE.blockComment)
                if (v) { tokens.push({ type: "comment", value: v, start: i, end: i + v.length }); i += v.length; continue }
            } else if ((v = eat(RE.regex))) {
                // Treat regex literal as a "string" for your minimal category set
                tokens.push({ type: "string", value: v, start: i, end: i + v.length }); i += v.length; continue
            }
        }

        // Strings
        if ((v = eat(RE.sng) || eat(RE.dbl) || eat(RE.bkt))) {
            tokens.push({ type: "string", value: v, start: i, end: i + v.length }); i += v.length; continue
        }
        // Numbers
        if ((v = eat(RE.number))) {
            tokens.push({ type: "number", value: v, start: i, end: i + v.length }); i += v.length; continue
        }
        // true/false/null/undefined
        if ((v = eat(RE.boolNullUndef))) {
            const t: TokenType = v === "true" || v === "false" ? "boolean" : (v === "null" ? "null" : "undefined")
            tokens.push({ type: t, value: v, start: i, end: i + v.length }); i += v.length; continue
        }
        // Keywords
        if ((v = eat(RE.keywords))) {
            tokens.push({ type: "keyword", value: v, start: i, end: i + v.length }); i += v.length; continue
        }
        // Identifiers
        if ((v = eat(RE.ident))) {
            tokens.push({ type: "identifier", value: v, start: i, end: i + v.length }); i += v.length; continue
        }
        // Punctuation / operators
        if ((v = eat(RE.punct))) {
            tokens.push({ type: "punctuation", value: v, start: i, end: i + v.length }); i += v.length; continue
        }
        // Whitespace
        if ((v = eat(RE.ws))) {
            tokens.push({ type: "whitespace", value: v, start: i, end: i + v.length }); i += v.length; continue
        }

        // Fallback
        if (src[i]) {
            tokens.push({ type: "unknown", value: src[i]!, start: i, end: i + 1 })
        }
        i += 1
    }

    return { type: "Program", tokens }
}

function tokenToHTML(token: Token): string {
    switch (token.type) {
        case "string": return `<span style="color: var(--red)">${escapeHtml(token.value)}</span>`
        case "number": return `<span style="color: var(--yellow)">${token.value}</span>`
        case "keyword": return `<span style="color: var(--purple)">${token.value}</span>`
        case "comment": return `<span style="color: var(--magenta)">${escapeHtml(token.value)}</span>`
        case "null": case "undefined": case "boolean":
            return `<span style="color: var(--green)">${token.value}</span>`
        case "punctuation": {
            // if (token.value === "(" || token.value === ")" || token.value === "{" || token.value === "}" || token.value === "[" || token.value === "]")
            //   return `<span style="color: var(--yellow)">${token.value}</span>`
            // else
            return escapeHtml(token.value)
        }
        case "identifier": {
            if (token.value[0]?.match(/[A-Z]/) || types.includes(token.value))
                return `<span style="color: var(--blue)">${token.value}</span>`
            else
                return `<span style="color: var(--cyan)">${token.value}</span>`
        }
        case "whitespace":
        case "unknown":
            return `${escapeHtml(token.value)}`
    }
}

export function escapeHtml(str: string): string {
    return str
        .replace(/&/g, "&amp;")
        .replace(/</g, "&lt;")
        .replace(/>/g, "&gt;")
        .replace(/"/g, "&quot;")
        .replace(/'/g, "&#39;")
}