import { _keyword, _assoc_BANG, Vector } from './types';

export class BlankException extends Error {}

class Reader {
    constructor(tokens) {
        this.tokens = tokens
        this.position = 0
    }
    next() { return this.tokens[this.position++] }
    peek() { return this.tokens[this.position] }
}

function tokenize(str) {
    const re = /[\s,]*(~@|[\[\]{}()'`~^@]|"(?:\\.|[^\\"])*"|;.*|[^\s\[\]{}('"`,;)]*)/g
    let match = null
    let results = []
    while ((match = re.exec(str)[1]) != '') {
        if (match[0] === ';') { continue }
        results.push(match)
    }
    return results
}

function read_atom (reader) {
    const token = reader.next()
    //console.log("read_atom:", token)
    if (token.match(/^-?[0-9]+$/)) {
        return parseInt(token,10)        // integer
    } else if (token.match(/^-?[0-9][0-9.]*$/)) {
        return parseFloat(token,10)     // float
    } else if (token[0] === "\"") {
        return token.slice(1,token.length-1)
            .replace(/\\(.)/g, (_, c) => c === "n" ? "\n" : c)
    } else if (token[0] === ":") {
        return _keyword(token.slice(1))
    } else if (token === "nil") {
        return null
    } else if (token === "true") {
        return true
    } else if (token === "false") {
        return false
    } else {
        return Symbol.for(token) // symbol
    }
}

// read list of tokens
function read_list(reader, start, end) {
    start = start || '('
    end = end || ')'
    var ast = []
    var token = reader.next()
    if (token !== start) {
        throw new Error("expected '" + start + "'")
    }
    while ((token = reader.peek()) !== end) {
        if (!token) {
            throw new Error("expected '" + end + "', got EOF")
        }
        ast.push(read_form(reader))
    }
    reader.next()
    return ast
}

// read vector of tokens
function read_vector(reader) {
    return Vector.from(read_list(reader, '[', ']'));
}

// read hash-map key/value pairs
function read_hash_map(reader) {
    return _assoc_BANG(new Map(), ...read_list(reader, '{', '}'))
}

function read_form(reader) {
    var token = reader.peek()
    switch (token) {
    // reader macros/transforms
    case ';': return null // Ignore comments
    case '\'': reader.next()
               return [Symbol.for('quote'), read_form(reader)]
    case '`': reader.next()
              return [Symbol.for('quasiquote'), read_form(reader)]
    case '~': reader.next()
              return [Symbol.for('unquote'), read_form(reader)]
    case '~@': reader.next()
               return [Symbol.for('splice-unquote'), read_form(reader)]
    case '^': reader.next()
              var meta = read_form(reader)
              return [Symbol.for('with-meta'), read_form(reader), meta]
    case '@': reader.next()
              return [Symbol.for('deref'), read_form(reader)]

    // list
    case ')': throw new Error("unexpected ')'")
    case '(': return read_list(reader)

    // vector
    case ']': throw new Error("unexpected ']'")
    case '[': return read_vector(reader)

    // hash-map
    case '}': throw new Error("unexpected '}'")
    case '{': return read_hash_map(reader)

    // atom
    default:  return read_atom(reader)
    }
}

export function read_str(str) {
    var tokens = tokenize(str)
    if (tokens.length === 0) { throw new BlankException() }
    return read_form(new Reader(tokens))
}