//! Turning schemas into the [`FieldDoc`]s the Docs tab renders: what type a

//! parameter or body field is, whether it's required, and which values it

//! accepts.

//!

//! This is a summary, not a spec viewer — the aim is answering "what can I put

//! here?" without leaving the terminal.

use std::collections::HashSet;

use serde_json::Value;

use super::resolve::deref;

use crate::model::FieldDoc;

/// Nesting cap when flattening a body schema. Also what terminates recursive

/// schemas, the same way [`super::examples`] caps generation depth.

const MAX_BODY_DEPTH: usize = 4;

/// Upper bound on body fields per request, so a sprawling schema can't turn

/// the Docs tab into thousands of lines.

const MAX_BODY_FIELDS: usize = 200;

/// Documentation for one OpenAPI parameter object.

pub fn param_doc(doc: &Value, p: &Value) -> FieldDoc {

    let location = p.get("in").and_then(Value::as_str).unwrap_or("query");

    let schema = p.get("schema").map(|s| deref(doc, s));

    let mut field = match schema {

        Some(schema) => field_doc(doc, schema),

        None => FieldDoc {

            ty: "string".into(),

            ..FieldDoc::default()

        },

    };

    field.name = p

        .get("name")

        .and_then(Value::as_str)

        .unwrap_or_default()

        .to_string();

    field.location = location.to_string();

    // Path parameters are required by definition (OpenAPI says so even when

    // the spec omits the flag).

    field.required =

        location == "path" || p.get("required").and_then(Value::as_bool).unwrap_or(false);

    // A description on the parameter beats one inherited from its schema.

    if let Some(d) = description(p) {

        field.description = Some(d);

    }

    field

}

/// Documentation for a request body schema, flattened to dotted paths:

/// `owner.name`, `pets[].tag`. A body that isn't an object gets a single row.

pub fn body_docs(doc: &Value, schema: &Value) -> Vec<FieldDoc> {

    let mut out = Vec::new();

    flatten(doc, schema, "", 0, &mut out);

    if out.is_empty() {

        let mut field = field_doc(doc, schema);

        if !field.ty.is_empty() && field.ty != "object" {

            field.name = "(body)".into();

            field.location = "body".into();

            out.push(field);

        }

    }

    out

}

fn flatten(doc: &Value, schema: &Value, prefix: &str, depth: usize, out: &mut Vec<FieldDoc>) {

    if depth > MAX_BODY_DEPTH || out.len() >= MAX_BODY_FIELDS {

        return;

    }

    let schema = deref(doc, schema);

    // An array contributes no fields of its own; describe its items under

    // `name[]` so the path reads like the JSON it documents.

    if let Some(items) = schema.get("items") {

        flatten(doc, items, &format!("{prefix}[]"), depth + 1, out);

        return;

    }

    for part in object_parts(doc, schema) {

        let required: HashSet<&str> = part

            .get("required")

            .and_then(Value::as_array)

            .map(|a| a.iter().filter_map(Value::as_str).collect())

            .unwrap_or_default();

        let Some(props) = part.get("properties").and_then(Value::as_object) else {

            continue;

        };

        for (name, sub) in props {

            if out.len() >= MAX_BODY_FIELDS {

                return;

            }

            let sub = deref(doc, sub);

            let path = if prefix.is_empty() {

                name.clone()

            } else {

                format!("{prefix}.{name}")

            };

            let mut field = field_doc(doc, sub);

            field.name = path.clone();

            field.location = "body".into();

            field.required = required.contains(name.as_str());

            out.push(field);

            // Scalars fall straight back out of this call.

            flatten(doc, sub, &path, depth + 1, out);

        }

    }

}

/// Schemas contributing properties to `schema`: itself, plus `allOf` members,

/// which OpenAPI uses for composition/inheritance.

fn object_parts<'a>(doc: &'a Value, schema: &'a Value) -> Vec<&'a Value> {

    let mut parts = vec![schema];

    if let Some(all) = schema.get("allOf").and_then(Value::as_array) {

        parts.extend(all.iter().map(|s| deref(doc, s)));

    }

    parts

}

/// Everything about a schema except the name and location, which only the

/// caller knows.

fn field_doc(doc: &Value, schema: &Value) -> FieldDoc {

    let schema = deref(doc, schema);

    FieldDoc {

        name: String::new(),

        location: String::new(),

        ty: type_label(doc, schema, 0),

        required: false,

        options: enum_options(doc, schema),

        description: description(schema),

        default: schema.get("default").map(scalar),

    }

}

/// A short, readable type: `string(uuid)`, `array<integer>`, `object`.

fn type_label(doc: &Value, schema: &Value, depth: usize) -> String {

    if depth > MAX_BODY_DEPTH {

        return "…".into();

    }

    let schema = deref(doc, schema);

    for key in ["oneOf", "anyOf"] {

        if let Some(alts) = schema.get(key).and_then(Value::as_array) {

            let labels: Vec<String> = alts

                .iter()

                .take(3)

                .map(|s| type_label(doc, s, depth + 1))

                .collect();

            let more = if alts.len() > 3 { " | …" } else { "" };

            return format!("{}{more}", labels.join(" | "));

        }

    }

    if schema.get("allOf").is_some() {

        return "object".into();

    }

    let types = type_names(schema);

    let Some(primary) = types.first() else {

        return if schema.get("properties").is_some() {

            "object".into()

        } else {

            "any".into()

        };

    };

    let mut label = match primary.as_str() {

        "array" => {

            let inner = schema

                .get("items")

                .map(|i| type_label(doc, i, depth + 1))

                .unwrap_or_else(|| "any".into());

            format!("array<{inner}>")

        }

        other => match schema.get("format").and_then(Value::as_str) {

            Some(f) => format!("{other}({f})"),

            None => other.to_string(),

        },

    };

    // OpenAPI 3.1 `type: [string, "null"]`.

    for extra in types.iter().skip(1) {

        label.push_str(" | ");

        label.push_str(extra);

    }

    label

}

/// `type` as a list — a plain string in 3.0, possibly an array in 3.1.

fn type_names(schema: &Value) -> Vec<String> {

    match schema.get("type") {

        Some(Value::String(s)) => vec![s.clone()],

        Some(Value::Array(a)) => a

            .iter()

            .filter_map(Value::as_str)

            .map(String::from)

            .collect(),

        _ => Vec::new(),

    }

}

/// Accepted values: the schema's own `enum`, or an array's item `enum` (the

/// options are what goes *in* the array either way).

fn enum_options(doc: &Value, schema: &Value) -> Vec<String> {

    let direct = schema.get("enum").and_then(Value::as_array);

    let from_items = || {

        deref(doc, schema.get("items")?)

            .get("enum")

            .and_then(Value::as_array)

    };

    direct

        .or_else(from_items)

        .map(|a| a.iter().map(scalar).collect())

        .unwrap_or_default()

}

fn description(v: &Value) -> Option<String> {

    let d = v.get("description").and_then(Value::as_str)?.trim();

    (!d.is_empty()).then(|| d.to_string())

}

/// Enum entries and defaults are shown as they'd be typed into a field, so

/// strings lose their quotes.

fn scalar(v: &Value) -> String {

    match v {

        Value::String(s) => s.clone(),

        other => other.to_string(),

    }

}

#[cfg(test)]

mod tests {

    use super::*;

    use serde_json::json;

    #[test]

    fn parameter_types_enums_and_requiredness() {

        let doc = json!({});

        let p = json!({

            "name": "status",

            "in": "query",

            "required": true,

            "description": "Status values to filter by",

            "schema": {"type": "string", "enum": ["available", "pending", "sold"], "default": "available"}

        });

        let d = param_doc(&doc, &p);

        assert_eq!(d.name, "status");

        assert_eq!(d.location, "query");

        assert_eq!(d.ty, "string");

        assert!(d.required);

        assert_eq!(d.options, ["available", "pending", "sold"]);

        assert_eq!(d.default.as_deref(), Some("available"));

        assert_eq!(d.description.as_deref(), Some("Status values to filter by"));

    }

    #[test]

    fn path_params_are_required_even_when_unflagged() {

        let doc = json!({});

        let p = json!({"name": "petId", "in": "path", "schema": {"type": "integer", "format": "int64"}});

        let d = param_doc(&doc, &p);

        assert!(d.required);

        assert_eq!(d.ty, "integer(int64)");

    }

    #[test]

    fn array_params_expose_item_options() {

        let doc = json!({});

        let p = json!({

            "name": "tags",

            "in": "query",

            "schema": {"type": "array", "items": {"type": "string", "enum": ["a", "b"]}}

        });

        let d = param_doc(&doc, &p);

        assert_eq!(d.ty, "array<string>");

        assert_eq!(d.options, ["a", "b"]);

    }

    #[test]

    fn body_is_flattened_to_dotted_paths() {

        let doc = json!({

            "components": {"schemas": {

                "Address": {"type": "object", "required": ["zip"], "properties": {

                    "zip": {"type": "string"}

                }}

            }}

        });

        let schema = json!({

            "type": "object",

            "required": ["name"],

            "properties": {

                "name": {"type": "string"},

                "owner": {"type": "object", "properties": {

                    "address": {"$ref": "#/components/schemas/Address"}

                }},

                "pets": {"type": "array", "items": {"type": "object", "properties": {

                    "tag": {"type": "string", "enum": ["cat", "dog"]}

                }}}

            }

        });

        let docs = body_docs(&doc, &schema);

        let names: Vec<&str> = docs.iter().map(|d| d.name.as_str()).collect();

        assert_eq!(

            names,

            [

                "name",

                "owner",

                "owner.address",

                "owner.address.zip",

                "pets",

                "pets[].tag"

            ]

        );

        assert!(docs[0].required);

        assert!(!docs[1].required);

        let zip = docs.iter().find(|d| d.name == "owner.address.zip").unwrap();

        assert!(zip.required, "requiredness comes from the owning object");

        let tag = docs.iter().find(|d| d.name == "pets[].tag").unwrap();

        assert_eq!(tag.options, ["cat", "dog"]);

        assert_eq!(

            docs.iter().find(|d| d.name == "pets").unwrap().ty,

            "array<object>"

        );

        assert!(docs.iter().all(|d| d.location == "body"));

    }

    #[test]

    fn all_of_members_contribute_fields() {

        let doc = json!({});

        let schema = json!({"allOf": [

            {"type": "object", "required": ["id"], "properties": {"id": {"type": "integer"}}},

            {"type": "object", "properties": {"note": {"type": "string"}}}

        ]});

        let docs = body_docs(&doc, &schema);

        let names: Vec<&str> = docs.iter().map(|d| d.name.as_str()).collect();

        assert_eq!(names, ["id", "note"]);

        assert!(docs[0].required);

    }

    #[test]

    fn non_object_body_gets_one_row() {

        let doc = json!({});

        let docs = body_docs(&doc, &json!({"type": "string", "format": "binary"}));

        assert_eq!(docs.len(), 1);

        assert_eq!(docs[0].name, "(body)");

        assert_eq!(docs[0].ty, "string(binary)");

    }

    #[test]

    fn recursive_schemas_terminate() {

        let doc = json!({

            "components": {"schemas": {

                "Node": {"type": "object", "properties": {

                    "child": {"$ref": "#/components/schemas/Node"}

                }}

            }}

        });

        let docs = body_docs(&doc, &json!({"$ref": "#/components/schemas/Node"}));

        assert!(!docs.is_empty());

        assert!(docs.len() <= MAX_BODY_DEPTH + 1, "{}", docs.len());

    }

    #[test]

    fn union_and_nullable_types_read_as_written() {

        let doc = json!({});

        assert_eq!(

            type_label(&doc, &json!({"type": ["string", "null"]}), 0),

            "string | null"

        );

        assert_eq!(

            type_label(

                &doc,

                &json!({"oneOf": [{"type": "string"}, {"type": "integer"}]}),

                0

            ),

            "string | integer"

        );

        assert_eq!(type_label(&doc, &json!({}), 0), "any");

    }

}